Some ventilation systems, such as heat recovery systems in which heat energy is extracted from an air flow leaving an enclosure, such as a building, stored and added to another air flow entering the enclosure at a later point of time, require that appropriate air flows can be generated in two opposite directions.
The typical solution to this problem is to provide the ventilation system with two or more air flow generators, which are oppositely oriented so that one or more air flow generators are used for generating air flows in one direction and one or more other air flow generators are used for generating air flows in the opposite direction.
Some solutions trying to save space and reduce costs include the use of a system of registers, which can be placed in different positions for directing the air flow through the ventilation system in one direction or the other while still passing through or by the air flow generator in the same direction. However, such register systems may be rather complicated and they are often not very stable and reliable as seen from a mechanically point of view.
Other solutions include the use of air flow generators which are able to generate air flows in two opposite directions, although not at the same time. However, such air flow generators typically have a primary and a secondary air flow direction, and the energy consumption for generating an air flow in the secondary direction may be twice as high as the energy consumption for generating a similar air flow in the primary direction. If the air flow generator is constructed to be “symmetric”, when it comes to generating air flows in the two directions, the efficiency of the air flow generator is typically rather poor in both directions.
Another problem of heat recovery systems known in the art is that the wind may force air inwards through the system, thus creating an air flow through the system, even in the opposite direction of the working direction of a weak air flow generator, if the pressure exerted by the wind exceeds the maximum possible working pressure of the air flow generator.
For this reason, some systems are provided with an inside register, which may be closed manually by a person, if the nuisances from the draught through the system become too severe.
It is an object of the present invention to provide a ventilation system, which overcomes the above-mentioned disadvantages of the systems known in the art.